1. Field of the Invention
The present invention relates to a recording medium such as a magnetic recording disk incorporated in a hard disk drive (HDD), for example. In particular, the invention relates to a writer or a method for writing head positioning or servo information into the recording medium.
2. Description of the Prior Art
A writing apparatus of head positioning information, such as a so-called servo track writer, is designed to utilize a magnetic head in writing head positioning or servo information into a magnetic recording disk. The magnetic head is usually mounted on a head slider. When the magnetic head finishes writing of the servo information for a single track, the head slider is forced to shift in the radial direction of the magnetic recording disk by a predetermined displacement amount. This movement serves to establish a predetermined interval or track pitch between adjacent tracks.
When the servo information is to be written into the magnetic recording disk, a spindle motor drives the magnetic recording disk for rotation about the driving shaft. The spindle motor inevitably suffers from a small vibration or eccentricity of the driving shaft during the rotation of the magnetic recording disk. This small vibration or eccentricity causes the magnetic head to deviate from the set circular orbit on the magnetic recording disk. The servo patterns are thus established on the magnetic recording disk off the expected circular track.
The interval or track pitch is expected to get reduced between adjacent tracks on the magnetic recording disk in the future. If the track pitch gets reduced, the aforementioned deviation of the magnetic head off the set orbit is supposed to lead to interference of the servo patterns, which are expected to establish the adjacent tracks. The later written servo pattern serves to erase the earlier written servo pattern. The interference of the servo patterns in this manner makes it impossible to correctly establish tracks on the magnetic recording disk based on the written servo patterns. Information data thus cannot correctly be written into the magnetic recording disk.